package com.java;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * 多个线程同时读一个资源类没有任何问题，所以为了满足并发量，读取共享资源应该可以同时进行
 * 但是
 * 如果有一个线程想去写共享资源，就不应该再有其他线程可以对该资源进行读或写
 * 小总结：
 *  读读能共存
 *  读写不能共存
 *  写写不能共存
 * @author jingjintao
 * @date 2021/10/24 - 23:21
 **/
public class ReadWriteLockDemo {
    public static void main(String[] args) {
        MyCache myCache = new MyCache();
        for (int i = 1; i <= 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                myCache.put(tempInt+"", tempInt+"");
            },String.valueOf(i)).start();
        }

        for (int i = 1; i <= 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                myCache.get(tempInt+"");
            },String.valueOf(i)).start();
        }
    }
}

class MyCache{

    private volatile Map<String, Object> map = new HashMap<>();
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void put(String key, Object value){
        readWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 开始写入数据 "+ key);
            map.put(key, value);
            try {
                TimeUnit.MILLISECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"\t 写入数据成功 ");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.writeLock().unlock();
        }

    }

    public void get(String key){
        readWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 开始读取数据 ");
            Object result = map.get(key);
            try {
                TimeUnit.MILLISECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"\t 读取数据成功 "+result);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.readLock().unlock();
        }

    }
}